Desmopressin, also known as dDAVP, is the therapeutically active ingredient (as its acetate salt) in the pharmaceutical product Minirin®, which is marketed inter alia as a nasal spray and a tablet formulation. Desmopressin is primarily used in the treatment of primary nocturnal enuresis, i.e. bedwetting, in children, but it is approved also for the treatment of nocturia and diabetes insipidus. The first market introduction of the tablet formulation was in Sweden in 1987.
In short, a solid dosage form such as a tablet formulation is typically manufactured by compression of a suitable granulate to the desired solid dosage form, where the granulate is composed of the required constituents as a mixture of solid particles. Typical such particles are the therapeutically active ingredient, various excipients, disintegrating agents, lubricants and binders, optionally together e.g. with flavoring agent, preservative and/or colorant. The commercially available Minirin® tablet is prepared according to this general protocol, and the tablet was first disclosed as set forth in the patent U.S. Pat. No. 5,047,398, the teachings of which are incorporated herein by reference. For a comprehensive overview of pharmaceutical tablet manufacturing, see “Tableting” (by N. A. Armstrong) in “Pharmaceutics—The science of dosage form design”, pp 647–668; Ed. M. E. Aulton, Churchill Livingstone, Edinburgh, London, Melbourne and New York, 1988, the entire teachings of which are incorporated herein by reference.
The Minirin® tablet that is currently marketed, and thus produced in industrial scale, consists of the therapeutically active ingredient desmopressin together with potato starch and lactose as excipients, and a suitable, amount of hinder and lubricant, respectively.
When preparing tablets, there is a general desire to obtain tablets that are as hard as possible (e.g. to reduce attrition in storage and handling) while avoiding detrimental effects on pharmaceutical properties such as disintegration time and drug release profile within the gastrointestinal tract. Moreover, a tablet should not be made so hard that it can not be chewed without, teeth damaging or otherwise excessive effort. If the tablets are prepared by compression of a granulate or a powder, additional care must also be taken to optimise the desired hardness in order to minimise machine wear and at the same time perform the compressing operation at the highest possible speed. Furthermore, in compressing operations one has to overcome the, problem that increased compression speed inherently tends to reduce the maximum attainable hardness.
In a compressing operation in a typical tabletting machinery, the tablets resulting from the compression of a granulate are ejected from the die in which they have been prepared by a punch, and the arising friction between the tablet and the die walls may thereby be considerable. Such friction may lead to an increased frequency of tablet rupture, i.e. in effect a waste of tablets, and also to increased wear of the tabletting machinery in general. It is therefore developed practice in the art to reduce the aforementioned friction by adding lubricant to powder or granulate that is to be compressed. For this purpose, a lubricant (magnesium stearate) is and has been present in the commercial Minirin® tablet in an amount of 0.50 percent by weight of the tablet.